Inter-body fusion is a commonly used technique to permanently attach vertebrae together to stabilize the spine in order to relieve nerve compression, stop pain, correct subluxation, correct scoliosis and repair damage from fractures and tumors. Typically the fusion is performed by removing disk material and damaged bone from between the vertebral bodies, putting a spacer or “fusion cage” between the vertebra to maintain the space between them and adding bone graft material into which new bone can grow to “fuse” the vertebrae together. An inter-body fusion of the lumbar spine can be performed anteriorly, posteriorly, inferiorly and laterally. Anterior approaches are complicated by having to work around the abdominal cavity and large blood vessels such as the aorta and vena cava. The anterior longitudinal ligament must be sacrificed in this approach and scoliosis cannot be effectively corrected because the lateral walls of the disk annulus cannot be released (cut) to correct lateral curvature of the spine related to degenerative changes in a disk. A posterior approach is compromised by the dural sac and spinal nerves. The posterior longitudinal ligament is often weakened and scoliosis cannot be corrected because the lateral walls of the annulus cannot be released. An inferior or “pre-sacral” approach is limited to the L4-L5 and L5-S1 disk levels and cannot be used to correct any significant amount of scoliosis. The lateral (direct lateral or extreme lateral) approach is compromised by the lumbar nerve roots but the annulus of the disk can be cut on each side, the anterior and posterior longitudinal ligaments preserved and a large inter-body cage can be placed to correct scoliosis or a lateral tilt of the spine. Inter-body fusions of the thoracic spine are done through the chest (transthoracic) or posterior laterally. The transthoracic approach is compromised by having to collapse a lung and work between the ribs. A posterolateral approach is compromised by the spinal cord and nerve roots. All of these approaches to the lumbar and thoracic spine for inter-body fusions are currently being done with minimally invasive techniques to minimize skin incisions and more importantly muscle damage.
Inter-body fusions are generally reinforced with plates or rods secured with bone screws. Pedicle screws and rods are most commonly used to reinforce inter-body fusions and to perform extensive corrections of lumbar and thoraco-lumbar scoliosis. Although one or two vertebral level pedicle screw and rod instrumentation can be reliably performed with minimally invasive techniques, more lengthy constructs generally require open operations to insert the screws and rods, especially if there is curvature of the spine. The advantages of anterior, inferior and lateral approaches for lumbar inter-body fusions and the advantages of trans-thoracic inter-body fusions are compromised by having to do a second operation from the back to reinforce the inter-body fusions. A lateral plate can be reliably placed to re-enforce a single level lateral lumber inter-body fusion, multiple level lumbar lateral plates are not currently feasible necessitating additional posterior pedicle screw and rod instrumentation. Lateral plates or rods have been placed over several levels in the thoracic spine via a trans-thoracic approach but not over longer distances.
Considering the advantages of lateral inter-body fusions in the lumbar and thoracic areas a multi-level lateral system to stabilize the spine in these areas would be of great utility to allow multi-level inter-body fusions of the thoracic and/or lumbar spine without an additional open posterior operation.